I have a doubt about the 'white spaces' in the maps from satellite. For example, for the atlantic areas I have plotted AOD and appear many areas where sistematically do not have any data (white spaces). So I want to know why that happens or which factors are behind that.

1 Answer
1

Expect every daily retrieval of AOD to have many missing pixels, mostly where clouds appear. Data is removed when the quality assurance flags do not meet some minimum criteria. This can happen when the retrieval is contaminated (e.g. from clouds or sun glint on the surface). If you are interested, you can obtain raw level-1 and level-2 data with all data, including arrays for quality assurance flags.

There will also be systematic gaps in the data where the satellite had no coverage. Polar orbiting satellites will get complete coverage near the poles, but widening gaps will appear the closer you get to the equator.

$\begingroup$I thank you for your answer. I uploaded an example (image) that helps understanding the nature of the question. I dont belive that the problem is caused by clouds because during 15 years, there was no record. I am waiting for your helping$\endgroup$
– Adilson Vladmir C. VeigaOct 6 '16 at 0:15

$\begingroup$If you are referring to the white stripe above 20 latitude, I don't know what that is. Perhaps this is a longitudinal slice, and that is a water feature? There are different algorithms used for "over land" and "over water" AOD, so depending on the data source, it might not include both. Or, perhaps it's a specific location with very high albedo (e.g. Sahara desert) where an AOD retrieval might have trouble.$\endgroup$
– farrenthorpeOct 6 '16 at 0:25

$\begingroup$the product is from terra-dark target-550nm and over a segment north-south in the atlantic ocean in the outflow of the african continent. really it is dificult to know the cause, but I believe that is something related to the retrieval$\endgroup$
– Adilson Vladmir C. VeigaOct 6 '16 at 0:59

$\begingroup$If it's over ocean, it could be an island or other piece of land. The over-land and over-ocean data are not necessarily in the same dataset.$\endgroup$
– farrenthorpeOct 6 '16 at 4:49